1. Field of the Invention
The invention relates to the settling stabilization of latex dispersion of polymer-containing particles in oil.
2. Description of the Prior Art
Water-soluble polymers are used in a variety of applications such as paper making, sludge dewatering, tertiary oil recovery and throughout the mining industry. In most applications, high molecular weight is desired for better performance. High molecular weight water-soluble polymers can be produced by an inverse dispersion polymerization process. This involves the emulsification of the water-soluble monomer in an organic continuous phase (water-in-oil). Polymerization is carried out with either oil or water-soluble initiators. Initiation occurs and the monomer inside the dispersed particles is consumed to give a polymer-containing particle. The advantages of inverse dispersion polymerization are high molecular weights, higher solids load and a low viscosity product.
One of the drawbacks of this dispersion product is that the polymer-containing particles, being more dense than the surrounding oil, settle on aging. This results in an oil layer at the top and sediment at the bottom of the container. A concentration gradient develops with low polymer concentration near the top and high polymer concentration near the bottom of the container. The product is of poor quality since the non-homogeneous product causes problems when feeding.
U.S. Pat. No. 3.915,920 issued to Slovinsky, et al. discloses an additive and method of stabilizing and decreasing sediment in a water-in-oil dispersion where the aqueous discontinuous phase contains a water-soluble vinyl addition polymer, comprising an oil-soluble polymer added to the continuous phase in the amount of about 0.1-1.0 percent by weight based on the total polymer dispersion. The additive and method are described as being useful for re-dispersing settled dispersions. Unfortunately, the method described within the '920 patent results in several problems with respect to practical application. Specifically, the product produced by the '920 method is difficult to manufacture since the additive only viscosities the latex with which it interacts. As a result, the latex stays highly viscous even when pumped, resulting in difficult pumping and dispersal of the latex once the additive has been combined with it.
Desirably a compound would exist that would stabilize a water-in-oil latex dispersion during storage, but would be easily pumpable when shear is applied to the stabilized latex.